Thread Tools
Nov 09, 2012, 05:45 PM
608 km/h!
josh18's Avatar
Ha ha, Ive done that too!
Sign up now
to remove ads between posts
Nov 12, 2012, 10:18 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Well I picked up the first wing molds today. These require some sanding and will be used as practice molds.

Also found a good core medium material, Endurathane. Only gives 2-3min working time, so all needs to be sorted before mixing
Nov 12, 2012, 11:58 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
That's really excellent news about the wing moulds! I'm working on options to get the Scratcho done but it hasn't been easy to find a "cost effective" way. Hopefully I'm onto something now.

Alex if the Endurathane is the same as the GP330 which it probably is, you'll find that the working time is actually a lot less - maybe 45 seconds from mixing, at best. Do a few test mixes and play with it on some plastic. When it gets to the point that it "deflates" when your finger touches it, you can't handle it any more. So you know that's how long you have to get it in. It will be much shorter in hot weather.

It's absolutely paramount that you smear it over all of the inside skin surfaces, both sides, to get perfect filling. Although it can expand 33 times, I've been using a ratio of about a 12 or 14th of the volume, so it gets some back pressure and this greatly improves the foam consistency. In the fins I've got down to 1/10th, clamping the moulds up very hard, and the foam turns out about as hard as balsa, which is great.

Although maybe this advice is no use if you're not planning to expand in the mould?!
Nov 13, 2012, 05:34 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Well I put some into the fin of the first fuse. It busted open the seams even though I had taped it in a few places. Then after it cured fully, it deflated a bit, collapsing the fin. Hmmm...
Nov 13, 2012, 06:54 PM
AvB
AvB
Wind, hill, ... I'm keen ...
AvB's Avatar
I thought you knew ... PU is dangerous for the force it can exert with expansion. I'd only use it in a strong mould, or if you pour it inside an unrestrained cavity, it needs a lot of space at the top to rise.
Nov 13, 2012, 08:32 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Well I only filled the tail, letting the rest expand out the wing cut-out. I know now.

Next one will be in the mold
Nov 19, 2012, 07:51 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Man, picked up the Fuse again yesterday, and the foam has shrunk even more! the tail is almost collapsed completely flat! I have no idea why it is doing it.
Nov 19, 2012, 08:43 PM
Auzzie built planks
timbuck's Avatar
Quote:
Originally Posted by ALEX HEWSON
Man, picked up the Fuse again yesterday, and the foam has shrunk even more! the tail is almost collapsed completely flat! I have no idea why it is doing it.
Bummer..sorry to here that.

A few things can cause this in PU foams..
1. Not mixing enough.. Mixing with drill fast is best. ( a lot of companies recommend this.
2. Temp..
Both the mix , and the material you joining it to must be with in a few deg of each other , to get bonding to happen. Otherwise they will Repell over time( days , weeks)
Also as it ages , over a few days or weeks , and gets cold the PU matrix can shrink as the small bubbles that make it up collaps.
3
Water...humidity . They need it to cure fully all the way though.
Often in a closed environment , some parts of the volume will not be as cured as the out side. Leaving the centre soft , or softish.. Leads to shrinking .
Doing open mold expansion , and then joining , takes all the random anomalies out of the equation. With the same result every time
Also adding water to the mix...( a few drops ) helps make sure the mix it alway cured all the way through..

Tim
Latest blog entry: More colours
Nov 19, 2012, 08:50 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Cheers, Tim. I may try the next in two halves, vac bag, cure then trim, pour PU into the open cavity, cure, trim flush and join
Nov 20, 2012, 02:30 AM
608 km/h!
josh18's Avatar
Hey Alex, I just use a spar made of a drinking straw wrapped in glass or carbon for my tails. you can put one close to the front and one near the back if you want extra strength. This is really easy and works every time. Might be a good way for you to get some fuses out while you master the foam.
Cheers mate, see you soon
Nov 20, 2012, 04:09 AM
Auzzie built planks
timbuck's Avatar
+1 ...
All my wh's just carbon tail with carbon sock foam spar's.. Running down along into the fuse , stops the weak point at the tail junction.
Latest blog entry: More colours
Nov 20, 2012, 12:17 PM
Remember... Fly for fun!
ALEX HEWSON's Avatar
Cool guys! Cheers
Oct 07, 2013, 06:46 AM
Remember... Fly for fun!
ALEX HEWSON's Avatar
I started waxing the molds for the RT42 again. I think during the FEST we might build one up.
Oct 07, 2013, 04:25 PM
Registered User
That's cool Alex, just goes to show how the FEST has grown as last year it was a foamy build
Oct 07, 2013, 06:06 PM
Dave Pope Manawatu NZ
pope's Avatar
Cool whos going to by that one.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion 10 in1 servo tester (professional servo tester) flydreamrc Radios 22 Dec 12, 2016 01:22 AM
Alert RT Models Beaver Pre-release build St. Martin Scale Kit/Scratch Built 86 Jun 29, 2008 04:01 PM
Build Log kin'Brilliant Build Pics (PU-RT) wdeighton Slope 30 Mar 18, 2008 02:38 AM
Discussion RT Models MIG-15 Build AeroDude Electric Ducted Fan Jet Talk 34 Mar 02, 2008 04:49 PM
Discussion RT Mig 15 Build nut Electric Ducted Fan Jet Talk 8 Jul 30, 2007 12:17 PM